Bright dip compositions for the treatment of steel



U 'ing, plastic coating or 3,296,141 BRIGHT DIP COMPOSITIONS FOR THE TREATMENT OF STEEL Wilbur A. Lieb, Sandusky, and Edward Billow, Northfield,

' Ohio, assignors, by direct and mesne assignments, to

R. Hull 8: Company, Inc., Cleveland, Ohio, at corporation of Ohio No Drawing. Filed Mar. 25, 1965, Ser. No. 442,821

' 8 Claims. (Cl. 252-793) This invention relates to compositions and processes for the treatment of metal surfaces. More specifically, it concerns aqueous solutions for surface brightening, activation and chemical polishing of low carbon steel prior to metal plating, phosphate coating, blackening or other finishing operations. In addition, the invention relates to new processes for the surface treatment of low carbon steel and to chemical compositions which may be mixed with hydrogen peroxide to form aqueous treating solutions to be employed in such processes.

It is generally necessary in the metal fabricating industries to subject a metal surface to various cleaning, pickling and other treating procedures prior to plating or coating the metal to provide it with a more durable or attractive surface. One general type of treating solution used for'such preparation of metal surfaces is known in the trade as a bright dip. Such bright dip solutions produce a chemical polishing and brightening of the metal surface, and activate the metal surface to make it more receptive and adherent to metal plating, corrosion-resisting coatings, plastic coatings or the like.

Many different forms of chemical compositions are used as treating dips for metal and specifically for the treatment of steel. The solutions earliest used to cleanse metal surfaces were simple solutions of mineral acids, such as hydrochloric or sulfuric acid. Acid salts, e.g., sodium bisulfate,'sodium acid phosphate and ammonium bifluoride, have also been used alone, or in conjunction with acids, to form acidic solutions used as metal treating dips. For example, US. 2,828,913 discloses a metal treating composition containing ammonium bifluoride and chromic acid or chromic acid salts. This composition is not only acidic in action, but also possesses oxidizing properties because of the chromic acid. Other solutions of acidic nature containing oxidizing materials, and particularly peroxygen compounds, are known to be useful for treating metal surfaces. Examples of metal treating dips containing hydrogen peroxide or other peroxide materials, plus acids, for the treatment of metals are disclosed in US. Patents 2,154,455; 2,613,141; 2,736,640 and 2,923,

608. Some of the compositions of these patents may be classified as bright dips.

The purpose of a bright dip, particularly when used on steel, is to chemically polish the exposed metal surface to make it bright and smooth while avoiding the need for mechanical finishing operations in order to provide a metal surface of satisfactory appearance and activity to enable the treated metal to be processed with subsequent finishing operations such as metal plating, phosphate coatthe like. Pickling solutions which employ simple mineral acid solutions are'not effective for this purpose because, although they may remove rust or bright dip solutions which contain peroxygen compounds in addition to acidic reagents generally produce a treated surface having high reflectivity, but metal surfaces treated I with such compositions often exhibit poor corrosion or 3,296,141 Patented J an. 3, 1067 surfaces and new procedures for metal surface treatment,

particularly for the brightening and activating of surface of low carbon steel.

Further objects include:

(1) The provision of steel bright dip compositions having good stability and relatively long useful life in which low carbon steels may be immersed to be brightened, chemically polished and activated to provide beneficial effects in subsequent finishing operations applied to the treated metal, e.g., metal plating, phosphate coating, blackening, drawing or forming operations.

(2) The provision of new methods for the surface treatment of low carbon steel to improve the steel surface for the subsequent electroplating, phosphating, blackening or similar finishing operations. I

(3) The provision of new steel bright dip compositions which may be used to treat low carbon steel prior to plating, to create bettercoverage, better metal plating distribution, more corrosion resistance and a brighter finish to the final plated article.

-(4) The provision of new steel bright dip compositions which may be used to treat low carbon steel prior to phosphating to create ultimate phosphate coatings that are more dense, have a finer grain structure and are more corrosion resistant than phosphate coating which would be produced by phosphating steel surfaces not so treated.

(5) The provision of acidic metal treating compositions that may be used to prepare metal surfaces for blackening so that amore even black surface can be obtained.

(6) The provision of new steel bright dip compositions which may be used to treat low carbon steel surfaces prior to metal plating so less plating metal is required to obtain necessary brightness and corrosion protection, to improve the ability of the plating bath to cover deeply recessed areas, to improve plating metal distribution and to improve the corrosion resistance of the finished work.

(7 T he provision of new metal treating compositions comprising peroxygen compounds having improved stability, enabling a maximum amount of metal surface to be treated for a given quantity of the treating solution.

(8) The provision of stable, dry granular mixtures that may be conveniently mixed with hydrogen peroxide to form steel bright dip baths.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments ofthe invention, are given by Wayof illustration only, since various changes and modifications within compositions comprising-ammonium bifluoride anda .per-

other scale, they do not leave the treated metal surface in oxygen compound selectedfrom the group consisting of hydrogen peroxide and urea peroxide, these ingredients being present in a weight ratio of ammonium bifluoride to peroxygen compound between about lrl and 10:32. The presence of urea in the treating composition is preferred and if hydrogen peroxide is employed as the peroxygen compound rather than urea'peroxide, then the composition advantageously also contains urea.

Ammonium bifiuoride 30-64 Urea -70 Hydrogen peroxide 35-105 Using urea peroxide as a component of the new compositions, they may advantageously comprise the following ingredients in the parts by weight specified:

Ammonium 'bifiuoride 30-64 Urea peroxide 30-100 Hydrogen peroxide 0-105 In commercial practice of the invention, such solutions are advantageously prepared by using a dry granular mixture of ammonium bifluon'de and urea'imixed in a weight ratio of between about 100:1 and 100:110. Such dry mixtures may be dissolved in water in a concentration of about 9 to ounces per gallon (68-113 gms./l.) and hydrogen peroxide added in the amount needed to provide a peroxide content of 7% by weight.

The new bright dip compositions of the invention are generally useable with all established metal treating installations and equipment. Thus, they may be used in both rack and bulk processing installations which operate either manually or automatically. The treatment of the metal in these bright dips will advantageously follow uormal cleaning and pickling cycles but will precede the finishing cycle. Use of these new solutions basically involves the preparation of an aqueous treating bath containing ingredients as specified above, adjusting the temperature of the bath to be between about 35 and 50 C. and simple immersion of the metal article in'the heated :bath until the desired surface quality is obtained. Immersion times between about and 120 seconds are preferable, the time of immersion generally being shorter the higher the temperature of the bath. However, immersion times in excess of two minutes may be advantageous in some installations.

As treatment of metal articles in a bath continues, the activity of the bath will decrease. When the processing time required to yield the desired surface increases to a point of inconvenience, addition of l/lO to 2/ 10, the initial addition of ammonium bifluoride, peroxide compound and urea, if used, should be made. After a long period of use, if such addition of reagents fails to rejuvenate the treating solution, it should be discarded and fresh solution prepared. Where the particular installation or metal treating procedure requires close control of the processing conditions, determination of hydrogen peroxide content by suitable analysis may be used periodically to provide accurate control of the new bright dips. Using such analytical procedure, solution reagents are added in the same proportions as in the original makeup of the solution to bring the solution up to necessary concentration.

A more complete understanding of the new bright dip compositions and their method of use may be had by reference to the following details of operations performed in accordance with the invention. In these examples, all parts and percentages are by weight unless otherwise specified.

Example I A dry granular mixture was prepared by charging 48 parts of ammonium bifluoride and 50 parts urea into a tumble mixer and mixing the ingredients together for sufiicient time to obtain a homogeneous dry granular product. The required amount of this mixture was then put into a polyethylene lined treating tank to give a concentration of 98 grams of product per liter of the solution when the tank would be filled to the desired operating level. Sufiicient water was then run into the tank to half fill it, following which hydrogen peroxide solution (35%) was added in suflicient quantity to give a final concentration of 20% by volume. Finally, further water was added to bring the surface of the solution in the tank up to Op eration level. v

Using an electrical immersion heater with automatic temperature control, the temperature of the bath was raised to 40 C. and small forgings of low carbon steel carried upon plastic coated racks which had been pre+ viously subjected to normal pickling were dipped into the solution contained in the polyethylene lined tank and held therein for one minute. In this short time,- the ex= posed metal surface acquired a bright, shiny appear ance. The treated steel articles carried on the racks were then quickly removed from the bright dip bath and trans-a ferred to another tank containing 1% hydrochloric acid solution. The steel articles were immersed in the acid dip for 30 seconds, then removed and passed to a nickel plating operation. The treated steel articles were found to plate quickly and evenly with the nickel metal readily covering even deeply recessed areas of the articles. The final plated articles were found to have improved brightness as compared with those which were subjected to the same pickling and plating operations in the absence of the bright dip process of the invention.

Example 11 Urea peroxide 60 Hydrogen peroxide, 15% by volume.

Small hardware pieces fabricated from SAE 1010 class. mild carbon steel contained in plastic coated basketii holders were dipped into the bath which had previously been heated to a temperature of 50 C. The hardware pieces were held in the bath for 40 seconds, then removed and quickly dipped into another tank containing 2% hydrochloric acid. The articles were held in the acid bath for 30 seconds, then removed and promptly transferred to a phosphate coating bath. The treated steel articles were coated with a thin, even layer of phosphate material using a standard phosphate coating operation. Following normal rinsing and drying of the phosphate coated articles, suitable samples were subjected to a salt spray chamber corrosion test procedure and compared by this corrosion test to identical phosphate coated articles that had been processed in identical fashion except for the omission of the short immersion in the bright dip solution of this invention. This corrosion testing demonstrated the articles which had received the new bright dip step to possess substantially improved corrosion resistance.

Foregoing Example 11 illustrates that bright dip baths in accordance with this invention may use urea peroxide as a source of the hydrogen peroxide. This appears to work equally as well as a bath containing a physical mixture of urea and hydrogen peroxide. Urea peroxide is a simple addition compound between urea and hydrogen peroxide, the granular powder containing about 35% by weight of the equivalent of hydrogen peroxide.

Hydrogen peroxide and other peroxides have a tendency to be unstable on storage, particularly when mixed 1 new bright dip solutions by admixture at the opportune time with hydrogen peroxide as illustrated in foregoing Example I. The use of urea in the treating bath reduces the tendency of the treated metal for flash tarnishing and increases the time before tarnishing begins on the treated metal surface. Such tarnishing may take place quite quickly because the metal surface, as a result of the bright dip treatment, is extremely active.

Small amounts of other ingredients may be included in the new bright dip compositions of this invention to obtain additional advantages commensurate with the known properties of the added materials. For example, water-soluble dyes or coloring agents may be included in order to give a distinctive color to the dyes to enable workmen to readily distinguish these solutions from others which might be used in a treating plant. Also, surfactants or leveling agents may be employed, particularly those of a non-ionic type. Small amounts of other metal treating reagents, such as chromic acid, may be added and known peroxide stabilizers may be included. Such added materials may comprise up to about by weight of the total active ingredients of the bright dip baths and, advantageously, will comprise between about 0.01 and 5 grams per liter of the treating solution.

These bright dip solutions are contemplated for use with a variety of metals, although they are primarily designed for use with low carbon steel, i.e., steel having a carbon content of 0.20% or less. In some instances, it may be desirable to adjust the pH to a value different from that naturally assumed by this solution containing the ingredients in the proportions as specified. This can be accomplished by adding a small amount of mineral acid such as hydrochloric, sulfuric or hydrofluoric acid or by the addition of small amounts of a basic material, such as sodium hydroxide.

Commercial peroxide containing 35% active material is the product most commonly available to provide the peroxide ingredient of the new compositions. Hydrogen peroxide of other concentrations is available and may be used, but the amount used in the treating baths should be adjusted accordingly. As with the case of all solutions containing hydrogen peroxide, the compositions of this invention give off oxygen slowly which can build up a pressure in a container. Accordingly, suitable precautions should be observed in handling these solutions to prevent pressure damage to a container in the event that the treating solutions are to be transported or stored in a closed container. The treating solutions are acidic and require that suitable safety precautions be observed in using and handling them, e.g., suitable protective clothing should be worn by workmen. Any suitable acid resistant processing equipment may be used for treating metal article in the bright dip baths, although plastic coated tanks, barrels, dip baskets and racks are recommended. Chlorinated rubber, polyvinyl chloride and polyolefins, such as polyethylene, make suitable coatings or lining materials for processing equipment.

The immersion of a metal article in the new treating baths produces a bright surface on low carbon steel very quickly, normally within 10 seconds to two minutes, depending upon the physical condition or appearance of the surface of the piece being treated. Thorough cleaning is important in using the new bright dip baths because they do not themselves constitute cleaning or pickling solutions and are not designed primarily for the removal of rust. Thorough rinsing of the article to be treated in the baths is recommended prior to dipping in order to avoid introducing contaminants into the bright dip baths which would lead to a shortening of their life. The chemical polishing and brightening action of the new solutions, although highly efiective, is relatively mild and with low carbon steel, the solutions remove only a negligible amount of metal and do not significantly change the dimensions of the metal article being treated.

The new tieating compositions and methods have been found to give significantly increased corrosion protection to nickel plated or phosphated mild carbon steel parts. Also, improved coverage and metal distribution is attained on cadmium and zinc plated parts. When used before brass plating directly on vsteel, when the brass deposit is used for bonding of rubber, it has been found that a better rubber bonding action is obtained. The new compositions and methods are advantageously used prior to cadmium, zinc, copper, nickel or other plating operations as well as prior to phosphating, blackening or other similar metal finishing operations.

The invention to be covered by this United States Letters Patent is defined by the following claims.

We claim:

1. A composition for brightening and activating the surface of low carbon steel for subsequent finishing operations consisting essentially of an aqueous solution of the following ingredients in the proportions specified:

Grams/liter Ammonium bifiuoride 48 Urea 50 Hydrogen peroxide 2. A composition for brightening and activating the surface of low carbon steel for subsequent finishing operations consisting essentially of an aqueous solution of the following ingredients in the proportions specified:

Grams/liter Ammonium bifiuoride 48 Urea peroxide 60 Hydrogen peroxide 60 3. A composition for treating the surface of steel consisting essentially of a mixture of the following ingredients in the parts by weight specified:

Ammonium bifiuoride 30-64 Urea 0-70 Hydrogen peroxide 35-105 Ammonium bifiuoride 30-64 Urea peroxide 30-100 Hydrogen peroxide 0-105 dissolved in sufficient water to give a peroxide concentration of about 7% by weight.

5. As a composition for use in the treatment of metal surface, an aqueous solution of a mixture consisting essentially of ammonium bifiuoride and a peroxide compound selected f-rom the group consisting of hydrogen peroxide and urea peroxide, said ingredients being present in a weight ratio of ammonium bifiuoride to peroxide compound between about 1:1 and 10:32.

6. As a composition for use in the treatment of metal surfaces, an aqueous solution of a mixture consisting essentially of ammonium bifiuoride, urea and a peroxide compound selected from the group consisting of hydrogen peroxide and urea peroxide, the ammonium bifiuoride and peroxide compound being present in a weight ratio of ammonium bifiuoride t-o peroxide compound between about 1:1 and 10:32 and the urea being present in amount up to 70 parts for each 64 parts of ammonuim 'bifluoride.

7. A composition for use in the treatment of metal surfaces by admixture with hydrogen peroxide to provide an aqueous bath consisting essentially of a dry granular mixture of ammonuim bifiuoride and urea mixed in the weight ratio of between about :1 and 100:110.

8. A composition for use in the treatment of metal surfaces by admixture with hydrogen peroxide to provide an aqueous bath consisting essentially of about equal parts by Weight ammonium bifluor'ide and urea.

References Cited by the Examiner UNITED STATES PATENTS Ogata 2524-793 Nex et a1. 252-396 Brite 25279.3 Schwarzenberger 252'79.3

OTHER REFERENCES Condensed Chemical Dictionary, Rose, 6th ed., page 10 SAMUEL H. BLECH, Primary Examiner.

ALBERT T. MEYERS, Examiner.

S. E. DARDEN, Assistant Examiner. 

3. A COMPOSITION FOR TREATING THE SURFACE OF STEEL CONSISTING ESSENTIALLY OF A MIXTURE OF THE FOLLOWING INGREDIENTS IN THE PARTS BY WEIGHT SPECIFIED:
 4. A COMPOSITION FOR TREATING THE SURFACE OF STEEL CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN THE PARTS BY WEIGHT SPECIFIED: 